Project SALVO and Beyond – Military Multiplex Cartridges

In November of 1962, Frankford Arsenal loaded a small quantity of .223 Duplex cartridges. This consisted of a forward bullet of 33 grains followed by a second 34 grain projectile. The velocity is quoted as 2,760 fps.

During the late ’60s, Frankford Arsenal experimented with the Low Noise Duplex Cartridge (LNDC). The earliest cartridges were loaded with a pair of 110 grain tungsten core slugs. The initial projectiles use a blunt round nose profile, but later efforts consist of a semi-spitzer shape.

During the late 1980s, Olin produced three different types of duplex 5.56x45mm ammo for Colt’s entry in the Advanced Combat Rifle (ACR) trials. The original version used a special long-neck case which held a saboted pair of tungsten sub-projectiles. An interim version switched back to the standard length case firing a saboted pair of 27 grain .158″ tungsten sub-projectiles. The final version used the standard case with a pair of .224″ projectiles weighing 35 grains (front) and 33 grains (rear), giving a velocity of ~2,900 fps. The Bodermansports.com website claims to have some of the ACR test ammo available. Reportedly, during Operation Desert Shield, the USMC approached Olin about making a production run of the full-bore 5.56mm duplex ammo. Olin declined.

.22/7.62x51mm (Experimental):

“Project SALVO” – The experimental .22/7.62x51mm (aka: .22 NATO) cartridge used a standard length case for the single projectile load. However, its pair of duplex variants were loaded in long-neck cases. One was loaded with two 35 grain projectiles (3,505 fps), while the other was loaded with a pair of 41 grain bullets (3,250 fps).

.22/.30-’06 (Experimental):

During SALVO II testing, a duplex .22-’06 cartridge was introduced. It used a long neck case holding a pair of 50 grain projectiles (2,975 fps).

6.35mm Frankford/Winchester SCHV (Experimental):

Dr. Carten’s brief sidetrack for an “optimum” 6.35mm SCHV cartridge also produced duplex variants. The 6.35mm cartridge cases were dimensionally similar to the .25 Remington. One case was left full-length (~2.08″) and loaded with 70 grain projectiles for both single and duplex loads. The slightly shorter case (~1.88″) was loaded with single 70 grain projectiles or a pair of 53 grain bullets for the duplex (2,600 fps). The single projectile loads were the FA-T124 (long) and FA-T116 (short). The duplex loads were the FA-T127 and FA-T115.

.25/7.62x51mm (Experimental):

“Project SALVO” – Experimental .25 caliber cartridges were also based on the 7.62x51mm case, with single projectile and duplex loadings. The duplex loads featured a pair of 61 grain projectiles @ 2,990 fps. Once again, the case lengths are different between the single projectile and duplex loads.

.27/7.62x51mm (Experimental):

“Project SALVO” – Experimental .27 caliber cartridges were also based on the 7.62x51mm case, with single projectile and duplex loadings. The duplex loads featured a pair of 71 grain projectiles @ 2,980 fps. Yet again, the case lengths are different between the single projectile and duplex loads.

7.5x54mm French:

Early editions of Jane’s Infantry Weapons reference an experimental triplex round, but mention no data concerning the projectile weights or velocity.

7.62mm NATO:

“Project SALVO” – An early duplex 7.62x51mm cartridge used a pair of 96 grain projectiles (2,560 fps) in a long necked case. However, the later T314E3 duplex load used a standard case. This was eventually type-classified as the M198 Duplex Ball, and is credited with two ~84 grain slugs at 2,750 fps.

“Salvo Squeezebore” – Used with a special barrel attachment, three 20 grain projectiles would be squeezed down to ~.15″, giving a velocity of 4,000 fps.

“Future Rifle Program” – An off-shoot of their earlier 9.53mm/10mm multiple fléchette cartridges, Winchester later applied the concept to the standard 7.62x51mm cartridge case. This version launched a trio of 10.2 grain fléchette via a puller sabot.

.30-40 Krag:

In 1900, R.W. Scott’s multiball (duplex and triplex bullet) designs were tested by Frankford Arsenal. Loaded by Winchester, the duplex load used a 117 grain and a 121 grain projectile. The triplex load consisted of three 77 grain projectiles. Powder was loaded between the bullets in hopes of ensuring separation within the bore.

A multiball (duplex) guard cartridge loaded by Frankford Arsenal was adopted in 1902. The two projectiles, which appear to be lead buckshot, weigh 42 grain each. The short overall length of cartridge would not allow it to feed reliably from the magazine. Instead, the cartridge was intended to be manually inserted into the chamber.

In 1903, Frankford Arsenal was tasked with developing a multiball cartridge which would function properly from magazines, particularly with Gatling guns. Initial experiments were based on an elongated case similar to a full cartridge length blank. This was loaded with three small lead balls. This was not satisfactory, so another load was designed using the standard service case. A single 42 grain ball was topped by a ~156 grain lead bullet.

.30-’03 Springfield:

Multiball (duplex) guard cartridge: The two projectiles, which appear to be lead buckshot, weigh 42 grain each. The cartridge is loaded with 43.5 grains of an unspecified powder. The short overall length of cartridge would not allow it to feed reliably from the magazine. Instead, the cartridge was intended to be manually inserted into the chamber.

In 1903, Frankford Arsenal was tasked with developing a multiball cartridge which would function properly from magazines, particularly with Gatling guns. Initial experiments were based on an elongated case similar to a full cartridge length blank. This was loaded with three small lead balls. This was not satisfactory, so another load was designed using the standard service case. A single 42 grain ball was topped by a ~156 grain lead bullet.

.30-’06 Springfield:

Harry Greener’s experiments in the UK also played with duplex and triplex loads for the .30-’06. The cases were reportedly supplied by Remington, but loaded in the UK. You can see some of the Greener and Project Salvo .30-’06 loads here.

“Project SALVO” – There were at least three different multi-projectile loads tested in long-necked .30-’06 cases. One used a pair of 110 grain projectiles (2,520 fps), another had two 96 grain bullets (2,630 fps), and the last possessed a trio of 66 grain slugs (2,640 fps). By the time of SALVO II, the duplex and triplex .30-’06 loads used standard cases. There is also mention of a duplex load using two 140 grain bullets, but the configuration is not specified.

From 1987 to 1988, McDonnell Douglas Helicopter Company (MDHC) participated in Phase II of the ACR Program. The MDHC Advanced Individual Weapon System (AIWS) used a plastic-cased, multiplex cartridge, dubbed a ‘chiclet’ due to its flat, rectangular box profile. Initial work involved duplex and triplex loadings of conventional projectiles, but due to high recoil, this was scaled back to multiplex fléchette loadings. This started with a .42 caliber five fléchette load, and was eventually whittled back to four and then three fléchette loaded in a .338 caliber sabot.

7.92x57mm Mauser:

There were at least three different duplex loads tested by the Germans late in the Second World War. Loaded at Finower Industry (headstamp “cg”), one cartridge used two of the “S Patrone” projectiles, another used one “S Patrone” projectile and a projectile from the 7.92x33mm Kurz Patrone, and the last used two Kurz Patrone projectiles. The later was considered the best, considered effective out to 300 meters. The muzzle velocity is reported at ~1,760 fps.

9x19mm:

“Salvo Squeezebore” – In a joint effort between Colt and IMI, a triplex squeezebore load was developed for a modified Uzi.

9.53mm/10mm Multiple Fléchette Cartridge (Experimental):

“Future Rifle Program” – In the late ’60s, Winchester developed a series of multiple fléchette cartridges, which launched from three to five fléchette via a pusher sabot. These cartridges were based on a proprietary straight-wall, belted cartridge case. By late 1970, Winchester finalized a 9.53mm variant using an aluminum cartridge case. The loadings included a standard four fléchette payload (4,240 fps), a pair of ‘ball’ fléchette paired with a tracer, and even a specialized armor piercing ‘penetrator’. Despite pushing pressures of up to 75,000 psi, the large bore volume limited this to a brief spike, allowing the aluminum cartridge case to remain intact.

.45 ACP:

“Salvo Squeezebore” – Used with a special barrel attachment, three 80 grain projectiles would be squeezed down to ~.38″.

.45 Revolver (Colt and S&W):

In the late 1870s, Captain E.M. Wright of Army Ordnance developed triplex and duplex multiball loads for Colt SAA and S&W Schofield revolvers. The cases were lengthened, nearly the same length as the standard cartridge’s overall loaded length. In 1878, Capt. Wright also played with a variation of his .45-70 triplex load in a modified Colt SAA.

In 1879, Merwin, Hulbert & Co. submitted their own triplex load based on the standard service cartridge case. The leading projectile weighed 112 grains while the two trailing projectiles weighed 83 grains each. The projectiles were contained within a waxed paper jacket, allowing the leading projectile to be seated completely outside the case mouth.

In 1889, the National Armory (Springfield) tested a third multiplex type, the Anderson Divided Bullet. Invented by Dr. L.B. Anderson, the load consisted of a standard profile projectile divided lengthwise into four equal slices. As could be expected, the projectiles showed excessive dispersion and poor penetration.

.45-70/.45 Government:

Frankford Arsenal, Union Metallic Cartridge (UMC) Company, and Remington each produced triplex multiball loads. Based on the work of Capt. E.M. Wright, the Frankford Arsenal loads used three 133 grain round balls and 45 grains of black powder. Examples of these have been found using a copper case and the Benét Cup Inside Primer. The UMC multiball loads date from 1902-03 and use conventional primers and brass cases. (It is alleged that UMC only provided the cases, and Frankford manufactured the rounds in question.) Remington produced two million multiball cartridges during 1917 as old Springfield Trapdoors were being reissued to guards at various military installations.

In 1879, Merwin, Hulbert & Co. submitted their own triplex and quadraplex loads. The leading projectile weighed 112 grains while the trailing projectiles weighed either 110 grains or 83 grains apiece. The projectiles were contained within a waxed paper jacket, allowing the leading projectile to be seated completely outside the case mouth. Phoenix Metallic Cartridge Co. also submitted similar triplex loads in the same year.

12.7x99mm (.50 BMG):

“Salvo Squeezebore” – Used with a special barrel attachment, five 140 grain projectiles would be squeezed down to ~.30″, giving a velocity of 3,050 fps.

12.7x107mm Soviet:

LVE (Novosibirsk) has offered the following:

Duplex API 1SL: 463 grain (front) and 478 grain (rear) at ~2460 fps.

Duplex API-T 1SLT: two 416 grain projectiles at ~2460 fps.

The Chinese now advertise the DVD06 featuring a 493 grain (front) and 556 grain (rear) at ~2,460 fps.

A TGZ reader asked for additional data concern­ing duplex and triplex loads developed during Project SALVO. Frank­ford Arsenal and Olin-Mathieson Chemical Co. (Winchester) were re­sponsible for creating a multitude of experimental multi-projectile loads for the SALVO tests. Many of the early examples used special long necked cases to give the same over-all loaded length as the parent cartridge. By the time of SALVO II, most used standard cartridge cases.

However, while Projectile SALVO was probably the most prolific era of duplex and triplex cartridges for military use, the creation of such cartridges pre­dates Project SALVO, and has continued since.

The multi-projectile projects are broken down by caliber.

– D.E.W.

An Interesting Vintage Reference…

Duplex Army Cartridge

I found your article on the Army duplex cartridge in the October (1964) issue very interesting. I thought your readers might like to read the views of your “British cousins” on this cartridge. The following was published in The Rifleman, the British shooting magazine, which reprinted it from the Sunday Times.

“The War Office at present doubts the need for the Duplex Cartridge… ‘the British Tommy has always been the most accurate rifleman in the world. The Americans aren’t so hot: they prob­ably need two bullets. We don’t… but we’re quite willing to listen politely.’

“Just in case their attitude might be construed as sour grapes, the War Office hints that Britain long ago developed a far superior form of duplex cartridge.”

This should rankle some Pentagon feathers!

– from Bill Carlisle of
Sherbrooke, Canada, in a letter to Guns Magazine
February 1965

With TGZ’s closure in early 2017, Dean encouraged me to find a new home for my scholarship so it wouldn’t be lost in the dustbin of the Internet. Loose Rounds has welcomed me with open arms. In the future, I intend to expand my legacy TGZ articles and add new contributions here at Loose Rounds.